Convolution files are used within various DSP solutions when you want to address room correction acoustics. You can create these files to be used with ffmpeg. For example, you can pass the following string:

ffmpeg convOut=-i conv_file.wav -lavfi afir

You can look at this as equalization in the digital domain. In essence, MPD will just have to pass these parameters to ffmpeg. It will not need to create these files.